EP 0 849 451 A2 has disclosed a method for operating a gas turbogroup, the gas turbogroup substantially comprising a compressor, a combustor, a turbine and a generator. Air that has been compressed in the compressor and fuel are mixed in a premixer of the combustor prior to combustion and are then burnt in a combustion chamber. Compressed air supplied via a partial air pipe is mixed with fuel supplied via a partial fuel pipe, and the mixture is introduced into a reactor having a catalytic coating. In the reactor, the fuel mixture is converted into a synthesis gas, comprising hydrogen, carbon monoxide, residual air and residual fuel. This synthesis gas is injected into zones of the combustor in which it stabilizes the flame. Injecting the synthesis gas, which is highly reactive on account of the hydrogen fractions, causes flames to form at the injection locations, consuming residual oxygen from the lean main combustion. This combustion reaction is relatively stable and moreover forms an ignition source for the main combustion, and consequently the flames from this reaction also serve as pilot flames.
U.S. Pat. No. 5,569,020 has disclosed a premix burner with a lance arranged concentrically in its head. At its outlet end, this lance includes a catalyst, which is designed to carry out full oxidation of a pilot fuel-oxidizer mixture flowing through it when the premix burner is operating. This generates a hot gas flow which is mixed with the cooler main fuel-oxidizer mixture of the premix burner and thereby stabilizes the combustion of the main fuel-oxidizer mixture. Since a hot gas flow is to be generated with the aid of the lance and the catalyst arranged therein, it is to be assumed that the fully oxidized mixture in the catalyst is lean.
Modern premix burners use a lean fuel-oxidizer mixture and have to be operated close to the ignition limit of their lean mixture in order to keep the formation of NOx at a low level and in order thereby to be able to comply with the evermore stringent regulations on emissions. Consequently, these burners are very susceptible to combustion instabilities and are moreover exposed to extensive pressure fluctuations, which has an adverse effect on the service lives of the burner, of a downstream combustor and of a gas turbine and its blades and vanes. It is therefore necessary to stabilize combustion in a lean mix premix burner.